Conformational Ensembles from Experimental Data and Computer Simulations

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Conformational Ensembles from Experimental Data
and Computer Simulations Poster Abstracts
135
98-POS Board 18
Partial Folding of Intrinsically Disordered Plant LEA Proteins is Required for Membrane
Binding and Stabilization
Anja Thalhammer1, Anne Bremer 2, Carlos Navarro-Retamal3, Gary Bryant4, Wendy González3,
Dirk K. Hincha2.
1University of Potsdam, Potsdam, Germany, 2Max-Planck Institute of Molecular Plant
Physiology, Potsdam, Germany, 3Universidad de Talca, Talca, Chile, 4RMIT University,
Melbourne, Australia.
Late embryogenesis abundant (LEA) proteins accumulate in seeds and vegetative plant tissues,
especially after exposure to abiotic stresses and in desiccation tolerant bacteria and invertebrates.
Their expression is directly linked to cellular dehydration as arising during freezing or
desiccation. Most LEA proteins are intrinsically disordered under fully hydrated conditions and
fold during drying. We focus on two cold-induced Arabidopsis thaliana LEA proteins, COR15A
and COR15B. Functionally redundant, COR15A and COR15B stabilize membranes during
freezing in vitro and in vivo while they do not stabilize selected enzymes during freezing in vivo.
Both proteins are disordered in solution, but fold into amphipathic α-helices in the dry state, as
shown by circular dichroism (CD) and fourier-transform infrared (FTIR) spectroscopy and in
silico analysis. The unfolding process of both COR15 proteins after transfer to water was
modeled by Molecular Dynamics simulations, using homology and threading modelling
approaches and showed quantitative agreement with experimental data. In water, unfolding was
driven by a break of intramolecular and concomitant formation of protein-water H-bonds. We
used glycerol as a low-molecular weight crowding agent to model reduced cellular water
availability. Experimentally, we found a concentration dependent gain of α-helical structure in
solutions containing glycerol. Unfolding of COR15A and COR15B as assessed by Molecular
Dynamics simulations was reduced in glycerol-containing systems, indicating that structural
stabilization can be explained by preferential exclusion of glycerol from the protein backbone.
FTIR spectroscopy, X-ray diffraction and Molecular Dynamics simulations further revealed that
COR15A associates with artificial membranes exclusively in an at least partially folded state.
Overall, our findings indicate an initial dehydration-induced folding step is necessary to render
the COR15 proteins competent for membrane interaction. A second folding step takes place
during membrane association.